1. Field of the Invention
The present invention relates to an organic electroluminescent display, and, more particularly, to an improved organic electroluminescent display of which the interior structure is prevented from being projected on an image forming portion through electrodes.
2. Description of the Related Art
Generally, organic electroluminescent displays are self-luminescent displays which emit light by electrically exciting a fluorescent organic compound. They can be operated with a low voltage, and can be made to be thin. In addition, organic electroluminescent displays have advantages, such as a wide viewing angle and a fast response speed, that overcome the problems of liquid crystal displays. Accordingly, they have been noted as next generation displays.
In the operation of organic electroluminescent displays, electrons are moved from a cathode to a luminescent layer via an electron transport layer, and holes are moved from an anode to the luminescent layer via a hole transport layer. The electrons meet the holes in the luminescent layer, which is organic and disposed between the cathode and the anode, thereby generating excitons having high energy. The excitons having high energy make transitions to having low energy, thereby producing light. Various colors can be implemented, depending on the type of organic material the luminescent layer is composed of.
In the meantime, the organic material used for organic electroluminescent displays is greatly influenced by moisture and oxygen. Moisture and oxygen cause many problems, such as degrading the characteristics of the organic material, lifting off a cathode, and shortening the life span of the organic electroluminescent display.
In order to protect the organic layer from moisture and impurities included in the air, organic electroluminescent displays are encapsulated. Encapsulation is implemented by bonding a metal cap or glass cap to a transparent substrate having an organic layer, using an adhesive.
Such encapsulation structures are disclosed in U.S. Pat. Nos. 5,059,862, 5,047,687, and 5,059,861. In these encapsulation structures, a capping layer is formed on the top surface of a dielectric layer. In Japanese Patent Publication hei 9-274990, a structure in which an organic layer is wrapped by a polyurethane encapsulation layer, which is wrapped by an external air blocking layer containing a desiccant, is disclosed. In a structure disclosed in U.S. Pat. No. 5,882,721, a glass sealing case is installed at a transparent substrate having an organic layer to wrap the organic layer, and a sealed space defined by the glass sealing case and the transparent substrate is filled with inert gas.
In the above-described encapsulation structures, a first electrode is formed of a transparent material, and a second electrode is formed by evaporating aluminum or the like, so the interior structure of an organic electroluminescent display may be exposed through the first and second electrodes. When the internal structure is projected on a transparent substrate on which an image is formed, there is a degradation in the resolution of the image.